The present invention relates to an antireflective coating composition, preferably a top antireflective coating composition, suitable for use with a photoresist; a process for producing such an antireflective coating composition; and a process for using such an antireflective coating composition in conjunction with a light-sensitive photoresist composition to produce semiconductors and other microelectronic devices. The present invention further relates to a process for coating substrates with such an antireflective coating composition, either before or after coating with a light-sensitive photoresist composition, as well as the process of coating, imaging and developing a light-sensitive photoresist composition in combination with such an antireflective coating composition on a substrate.
Thin film interference plays a central role in process control for optical microlithography utilized in producing microelectronic devices. Small variations in the thickness of a photoresist coating, or of thin films coated over or underneath the photoresist, can cause large exposure variations, which in turn usually cause two classes of undesirable line width variations.
1 . As thin film thickness may vary from run to run, wafer to wafer, or across a wafer, line widths will vary from run to run, wafer to wafer or across a wafer. PA1 2. As patterning takes place over the wafer topography, the photoresist coating thickness unavoidably changes at the topography edge, causing the line width to vary as it crosses the edge. PA1 R.sub.3 is a methyl, ethyl, propyl or butyl group PA1 R.sub.4 -R.sub.7 are independently hydrogen, or C.sub.1 to C.sub.5 alkyl PA1 n=10 to 50,000 PA1 R.sub.3 is a methyl, ethyl, propyl or butyl group PA1 R.sub.4 -R.sub.7 are independently hydrogen, or C.sub.1 to C.sub.5 alkyl PA1 n=10 to 50,000 PA1 (1) from about 1% to about 5%, preferably from about 1% to about 3%, of the polymer from step a), having a weight average molecular weight ("Mw") of from about 1000 to 500,000, preferably from about 2000 to 500,000, most preferably from about 5000 to 500,000; PA1 (2) from about 2% to about 10%, preferably from about 2% to about 5%, of a fluorine-containing, sparingly water-soluble (0.1%-10% by weight in water, preferably 0.5%-5% by weight) organic C.sub.3 -C.sub.13 aliphatic carboxylic acid; PA1 (3) from about 0.5% to about 3%, preferably from about 0.5% to about 1.5%, of a non-metallic hydroxide, such as an ammonium hydroxide, preferably a tetramethyl ammonium hydroxide; and PA1 (4) at least 85%, preferably at least 90%, of a solvent, preferably deionized ("DI") water . PA1 R.sub.3 is a methyl, ethyl, propyl or butyl group PA1 R.sub.4 -R.sub.7 are independently hydrogen, or C.sub.1 to C.sub.5 alkyl PA1 n=10 to 50,000 PA1 (1) from about 1% to about 5%, preferably from about 1% to about 3%, of the polymer from step a), having a weight average molecular weight ("M.sub.w ") of from about 1000 to 500,000, preferably from about 2000 to 500,000, most preferably from about 5000 to 500,000; PA1 (2) from about 2% to about 10%, preferably from about 2% to about 5%, of a fluorine-containing, sparingly water-soluble (0.1%-10% by weight in water, preferably 0.5%-5% by weight) organic (C.sub.3 -C,.sub.3) aliphatic carboxylic acid; PA1 (3) from about 0.5% to about 3%, preferably from about 0.5% to about 1.5%, of a non-metallic hydroxide, such as an ammonium hydroxide, preferably a tetramethyl ammonium hydroxide; and PA1 (4) at least 85%, preferably at least 90%, of a solvent, preferably DI water . PA1 (e) exposing the coated substrate from step d) to radiation, e.g., ultraviolet radiation, at a wavelength of from about 300 nm to about 450 nm, x-ray, electron beam, ion beam or laser radiation, in any desired pattern, such as those produced by the use of suitable masks, negatives, stencils, templates, etc.; PA1 (f) optionally subjecting the substrate from step e) to a post exposure second baking or heat treatment either before or after development; PA1 (g) developing the exposed photoresist-coated substrate from step e) either before or after the post exposure second baking of step f) to remove the image-wise exposed areas of a positive photoresist, or the unexposed areas of a negative photoresist.
Avoiding such thin film interference effects is one of the key advantages of advanced processes such as x-ray lithography or multi-layer photoresist systems. However, Single Layer Resist (SLR) processes dominate manufacturing lines for producing semiconductors and other microelectronic devices, because of the their simplicity, better cost-effectiveness, and the relative cleanliness of wet developing processes when compared with dry processes.
Thin film interference results in periodic undulations in a plot of the exposure dose required to clear a positive photoresist (Dose To Clear) versus the photoresist coating thickness. Optically, on a photoresist-coated substrate, light is reflected from the bottom reflective surface ("mirror", which is caused by the effect of the substrate +thin films), which interferes with the refection of light from the top mirror (the photoresist/air interface). As optical lithography pushes towards shorter exposure wavelengths, thin film interference effects become increasingly more important. More severe swings in the intensity of such thin film interference are seen as the exposure wavelength decreases.
In the past, dyed photoresists have been utilized to attempt to solve these reflectivity problems. However, it is generally known that dyed photoresists only reduce reflectivity from the substrate, but do not substantially eliminate it. In addition, dyed photoresists frequently cause a reduction in the lithographic performance of the photoresist, together with possible sublimation of the dye and incompatibility of the dye with the other components in photoresist films. In cases where further reduction or substantial elimination of the swing ratio is required, an antireflective coating material is coated onto the substrate prior to or after coating with the photoresist, and prior to exposure. The photoresist is imagewise exposed to radiation and then developed. The antireflective coating in the exposed area is subsequently etched either before the photoresist (top antireflective coating) or after the photoresist (bottom antireflective coating), typically in an oxygen plasma, and the photoresist pattern is thereby transferred to the substrate. The etch rate of the antireflective coating should be relatively high in comparison to the photoresist, so that the antireflective coating is etched without excessive loss of the unexposed protective photoresist film during the etch process.
Antireflective coating compositions containing a dye for absorption of the light and an organic polymer to provide good coating properties are known in the prior art. However, the possibility of sublimation and/or diffusion of the dye into the environment and/or into the adjacent photoresist layer, during heating, make these types of antireflective coating compositions less desirable.
Polymeric organic antireflective coating compositions are known in the art, as described in EP 583,205, which is incorporated herein by reference. However, such antireflective coating compositions are cast from organic solvents, such as cyclohexanone and cyclopentanone. A concern with the potential hazards of working with antireflective coating materials containing such organic solvents was one reason that led to the development of the antireflective coating composition of the present invention.
Photoresist compositions are used in microlithography processes for making miniaturized electronic components such as in the fabrication of computer chips, memory devices and integrated circuits. Generally, in these processes, a thin film of a photoresist composition is first applied to a substrate, such as a silicon wafer used for making integrated circuits and other microelectronic devices. The coated substrate is then baked to substantially evaporate the photoresist solvent in the photoresist composition and to fix (improve adhesion) the coating of photoresist onto the substrate. The baked, coated surface of the substrate is next subjected to an image-wise exposure to radiation, normally actinic radiation.
In a positive-working photoresist composition, this exposure to radiation causes a chemical transformation in the exposed areas of the coated surface. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in such microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed (positive-working photoresist) or the unexposed areas (negative-working photoresist) of the photoresist from the surface of the substrate. Visible light, ultraviolet (UV) light, electron beam and X-ray radiant energy are radiation types commonly used today in microlithographic processes. After this image-wise exposure, the coated substrate is treated with a developer solution to dissolve and remove either the radiation-exposed or the unexposed areas of the photoresist and all of the antireflective coating from the surface of the substrate.
When negative-working photoresist compositions are exposed image-wise to radiation, the areas of the resist composition exposed to the radiation become less soluble to a developer solution (e.g. a cross-linking reaction occurs) while the unexposed areas of the photoresist coating remain relatively soluble to such a solution. Thus, treatment of an exposed negative-working resist with a developer causes removal of the non-exposed areas of the photoresist coating and the creation of a negative image in the coating, thereby uncovering a desired portion of the underlying substrate surface on which the photoresist composition was deposited.
After development, the now partially unprotected substrate may be treated with a substrate-etchant solution or plasma gases and the like. The etchant solution or plasma gases etch that portion of the substrate where the photoresist coating was removed during development. The areas of the substrate where the photoresist coating still remains are protected and, thus, an etched pattern is created in the substrate material which corresponds to the photomask used for the image-wise exposure of the radiation. Later, the remaining areas of the photoresist coating may be removed during a stripping operation, leaving a clean etched substrate surface. In some instances, it is desirable to heat treat the remaining photoresist layer, after the development step and before the etching step, to increase its adhesion to the underlying substrate and its resistance to etching solutions.
Positive working photoresist compositions are currently favored over negative working resists because the former generally have better resolution capabilities and pattern transfer characteristics. Photoresist resolution is defined as the smallest feature which the resist composition can transfer from the photomask to the substrate with a high degree of image edge acuity after exposure and development. In many manufacturing applications today, resist resolution on the order of less then one-half micron are necessary. In addition, it is almost always desirable that the developed photoresist wall profiles be near vertical relative to the substrate. Such demarcations between developed and undeveloped areas of the resist coating translate into accurate pattern transfer of the mask image onto the substrate.